Knowledge Bank

FeH, produced by reaction of $FeCO5$ with H atoms, has been studied by selective laser-induced fluorescence following excitation of single rotational levels of individual spin-orbit components of $v=0$ of $e6\Pi$. As well as lines of known transitions including $c6\Pi -a6\Delta$, a number of transitions to a new lower state have been recognized. This state lies at about 0.5 eV above the ground state; rotational structure, recorded at high resolution, shows strong R and P branches and very weak Q lines. The apparent value of the rotational constant, B, is very small, $\sim 3.5cm-1$, not much more than half of the expected, unperturbed value.